This article is only relevant for WSS 3.0 and MOSS 2007.
When there is a requirement to customise the appearance of a SharePoint site, the first consideration is the version being used.
Branding WSS sites
If the SharePoint version is WSS (free to install if you have Windows Server 2003), colour and image changes are possible along with minor layout changes. It is not possible to use WSS to produce an accessible SharePoint site.
The default theme of SharePoint looks like the following
Other built-in themes that have different colours and images only are available
Microsoft released 10 new themes for SharePoint in March 2009 and one of these could be used. Again, the structure of the site is the same and only colour and images have changed.